I like the survey questions. Perhaps another way to ask the hours/night question might be to ask what percentage of the night do you sleep using your CPAP? Alternatively, "On average, how many hours do you sleep per night using your CPAP", and also "how many hours per night do you sleep without your CPAP"
I am a Neuroscience professor, and also a sleep apnea patient. I suffered from sleep apnea for approximately 15 years, but have only been treated with CPAP for the past 5 years after self-diagnosing the problem. The increase in my energy and cognition is amazing since I started using a CPAP, and am only disappointed in how long it took to get the diagnosis. I look at using the CPAP like wearing glasses, I’d rather sleep without it, but I feel so much better using it.